[ros-users] roslua: creating messages with subtypes

[Markus Klotzbuecher]

On Tue, Feb 22, 2011 at 07:36:08AM +0100, Steven Bellens wrote:
> 2011/2/21 Markus Klotzbuecher <markus.klotzbuecher at mech.kuleuven.be>:
> > Dear List,
> >
> > I just gave roslua a try and its working quite nicely. One smaller
> > problem I noticed is when printing some array types:
> >
> > $ lua -lroslua
> > Lua 5.1.4  Copyright (C) 1994-2008 Lua.org, PUC-Rio
> >> twist = roslua.get_msgspec("geometry_msgs/Twist")
> >> t=twist:instantiate()
> >> t:print()
> > geometry_msgs/Twist
> > /home/mk/src/git/lua/roslua/src/roslua/msg_spec.lua:53: attempt to call method 'find' (a nil value)
> > stack traceback:
> >      /home/mk/src/git/lua/roslua/src/roslua/msg_spec.lua:53: in function 'is_array_type'
> >      /home/mk/src/git/lua/roslua/src/roslua/message.lua:259: in function 'print_value'
> >      /home/mk/src/git/lua/roslua/src/roslua/message.lua:285: in function 'print'
> >      stdin:1: in main chunk
> >      [C]: ?
> >>
> >
> > Secondly I wondered if there is a more compact way to create messages
> > which contain submessages. For instance to create and fill a
> > "geometry_msgs/Twist" I did the following:
> >
> > local Vector3=roslua.get_msgspec("geometry_msgs/Vector3")
> >
> > local m = p.msgspec:instantiate() -- geometry_msgs/Twist message
> > local vec3lin = Vector3:instantiate()
> > local vec3ang = Vector3:instantiate()
> >
> > vec3lin.values.x=x
> > vec3lin.values.y=y
> > vec3lin.values.z=z
> > vec3ang.values.x=xang
> > vec3ang.values.y=yang
> > vec3ang.values.z=zang
> >
> > m.values.linear = vec3lin
> > m.values.angular = vec3ang
> >
> >
> > Before that I tried
> >
> > m.values.linear.x = x
> > m.values.linear.y = y
> > ...
> >
> > but this didn't work.
> 
> What is the 'values' for?
> How about
> 
> m.linear.x = x
> m.linear.y = y   ?

The 'values' field is a Lua table which contains the message
variables, so I believe this is correct. But it's not clear how to set
fields if the submessage is not primitive, as in above case.

Best regards
Markus